The achievement of an ideal container closure requires application of seemingly conflicting design criteria. Thus, a closure must be configured to engage in positive sealing relationship with the rim of its container and yet be capable of relatively convenient removal. Also, the closure must possess sufficient flexural capacity to absorb impact forces (from any direction) which are likely to be encountered in service, without the sealing relationship being broken, and yet be sufficiently rigid to support static loads imposed by stacking of loaded containers.
Australian Patent Specification No. 435,466 (W.H. Roper et al) discloses a container-closure arrangement which, apparently, meets some but not all of the above requirements. The referenced patent specification describes one structure in particular (see FIG. 8 of the drawings of the patent specification) which provides for sealing of the closure to the rim of the container and for transfer of a static load from the closure to the wall of the container, the load transfer being provided for by a channel portion of the closure engaging in compression against a ledge portion of the container wall. The load transfer effect is enhanced by the walls of the channel being interconnected by radially extending ribs, but it is thought that these must have the effect of reducing the capacity of the structure to withstand impact forces without the closure-to-container seal being broken.